Casings are pipe run from the surface with the purpose of lining the walls of a drilled well. API Buttress thread casings may be furnished with a buttress thread and with or without coupling. Coupling threads, gauging practice and thread inspection should conform to the requirements of API Spec 5B. Thread Check, Inc. offers the complete range of API Thread Plug and Ring Gages to API Spec 5B. Our engineering staff have served on various API gaging subcommittees and have worked in the energy industry for many decades. Thread Check's expert engineers can assist you with engineering and building custom gages. Thread Check is a proud member of the American Petroleum Institute.